Steam generating units or petrochemical process plants require large numbers of wet cooling towers to cool water used in steam condensing or other heat exchange applications. This water is typically cooled by evaporation, such as by co-mingling with air supplied by large multi-bladed fans. In this process, some water droplets are entrained in the air and come into contact with the leading edges of the fan blades. These fan blades will generally be moving at a very high velocity, typically 125 mph at the outer-most radius of the blade, and thus, over time, damage to these blades will occur.
The most troublesome problem with the fans used in these wet cooling towers is leading edge erosion which is caused by impact with the water droplets entrained in the air stream. Severe erosion by such impact can result in the loss of these fan blades costing $1,000.00 or more in replacement costs. One technique for preventing such erosion is to apply a rubber "boot" to the leading edge of each blade in order to absorb the impact energy of colliding with the droplets. The cost of this rubber boot is approximately $200 to $500 per blade with this cost including about four hours labor for installation. Thus, when considerinq the vast number of blades to be corrected, the cost and effort involved is quite substantial.
There is also an ongoing debate as to whether the erosion problem is due to faults in the blade or due to excessive water droplets in the air which compounds the difficulty of correcting the resultant problem.